Geometric analysis and timing of structures on mafic–ultramafic bodies and high grade metamorphic rocks in the Sierras Grandes of San Luis Province, Argentina

Abstract The study area comprises a portion of the Sierras Grandes of San Luis Province in west-central Argentina. This sector is composed of high-grade granulite facies metamorphic rocks, mainly gneisses and migmatites, with intercalated igneous mafic–ultramafic bodies. These bodies occur as discontinuous lenses along a narrow central belt concordant with the general NE–SW structural trend. The granulite facies metamorphism reached by this central area has been ascribed to the intrusion of the mafic–ultramafic bodies into an amphibolite facies metamorphic sequence. On both sides of the mafic–ultramafic bodies, a decrease of metamorphic grade to amphibolite facies is apparent. Numerous pegmatitic bodies intruding the metamorphic complex can be found elsewhere and, towards the western limit of the study area, La Escalerilla metagranite constitutes one of the larger granitic exposures of the Sierras. The results of the structural analysis, done along cross-sections transverse to the mafic–ultramafic belt, allow us to establish a structural evolution for this large geological feature. The described deformational events can be correlated with the tectonic framework postulated for the southern Pampean Ranges.